To avoid Zika virus, CDC says pregnant women should use condoms or abstain from sex

The Centers for Disease Control and Prevention (CDC) on Friday issued new interim guidance for the prevention of sexual transmission of the Zika virus, as well as new interim guidance for health care providers to use in taking care of pregnant women and women of reproductive age.

The sexual guidelines apply to "all methods" of sexual contact between males who have traveled to areas where active Zika transmission is taking place and pregnant women. This means oral, anal and vaginal sex.

The sexual guidelines come in the wake of a case in Dallas in which the virus was spread via sexual contact between a traveler returning from a Zika-affected country and a non-traveler.

The new guidelines say that pregnant women who have traveled to a country where active Zika virus transmission is taking place should be tested for the virus between two and 12 weeks after returning from such travel.

See images of the virus affecting newborns in Brazil:

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Zika, Mosquito borne illness causing birth defects in Brazil

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To avoid Zika virus, CDC says pregnant women should use condoms or abstain from sex

RECIFE, BRAZIL - JANUARY 29: Dr. Valeria Barros treats a 6-week old baby born with microcephaly at the Lessa de Andrade polyclinic during a physical therapy session on January 29, 2016 in Recife, Pernambuco state, Brazil. Health officials believe as many as 100,000 people have been exposed to the Zika virus in Recife, although most never develop symptoms. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 31: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is held by her mother Nadja Cristina Gomes Bezerra on January 31, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 29: David Henrique Ferreira, 5 months, who was born with microcephaly, is kissed by his mother Mylene Helena Ferreira on January 29, 2016 in Recife, Pernambuco state, Brazil. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 29: David Henrique Ferreira, 5 months, who was born with microcephaly, is held by his grandmother Maria Elisabeth as his mother stands at right on January 29, 2016 in Recife, Pernambuco state, Brazil. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)

Pregnant woman Angelica Prato, infected by the Zika virus, is attended at the Erasmo Meoz University Hospital in Cucuta, Colombia, on January 25, 2016. Authorities in Brazil, Colombia, Ecuador, El Salvador and Jamaica have advised couples to avoid pregnancy for the time being due to the presence of the Zika virus because if a pregnant woman is infected by the virus, the baby could be born with microcephaly. The Zika virus, a mosquito-borne disease suspected of causing serious birth defects, is expected to spread to all countries in the Americas except Canada and Chile, the World Health Organization said. AFP PHOTO/Schneyder Mendoza / AFP / SCHNEYDER MENDOZA (Photo credit should read SCHNEYDER MENDOZA/AFP/Getty Images)

RECIFE, BRAZIL - JANUARY 27: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is placed in her crib by her father Joao Batista Bezerra on January 27, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 26: Grandmother Ivalda Caetano holds Ludmilla Hadassa Dias de Vasconcelos (2 months), who has microcephaly, at Oswald Cruz hospital on January 26, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. The Brazilian government announced it will deploy more than 200,000 troops to combat the mosquitos which are spreading the Zika virus. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 27: Dr. Vanessa Van Der Linden, the neuro-pediatrician who first recognized and alerted authorities over the microcephaly crisis in Brazil, measures the head of a 2-month-old baby with microcephaly on January 27, 2016 in Recife, Brazil. The baby's mother was diagnosed with having the Zika virus during her pregnancy. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. At least twelve cases in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 31: Alice Vitoria Gomes Bezerra, 3-months-old, who has microcephaly, is held by her mother Nadja Cristina Gomes Bezerra on January 31, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 25: Estafany Perreira holds her nephew David Henrique Ferreira, 5 months, who has microcephaly, on January 25, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. Microcephaly results in newborns with abnormally small heads and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to further spread in South, Central and North America. At least twelve cases of Zika in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)

RECIFE, BRAZIL - JANUARY 25: Mother Mylene Helena Ferreira cares for her son David Henrique Ferreira, 5 months, who has microcephaly, on January 25, 2016 in Recife, Brazil. In the last four months, authorities have recorded close to 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. Microcephaly results in newborns with abnormally small heads and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to further spread in South, Central and North America. At least twelve cases of Zika in the United States have now been confirmed by the CDC. (Photo by Mario Tama/Getty Images)

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It also says pregnant women should use condoms to prevent the spread of Zika, or consider abstaining from sex for the duration of their pregnancy.

According to the CDC:

The CDC's guidance does not specifically call for abstinence as the preferred or only option in situations involving pregnant or non-pregnant sexual partners, although it does say it should be "considered" along with consistent use of latex condoms for concerned couples.

There have only been three cases on record in the medical literature in which the Zika virus has been spread by sexual contact or blood transfusions, meaning that mosquitoes are most likely causing the vast majority of cases, said CDC director Tom Frieden in a press conference call.

The virus is mainly spread by the widely distributed Aedes aegypti mosquito, which is an aggressive daytime biter and can be found in parts of North America as well as most of Central and South America. This mosquito species also carries other viruses, including Dengue and Chikungunya.

Frieden said there is increasing evidence that the Zika virus causes a devastating birth defect known as microcephaly, in which babies are born with smaller than average heads and incomplete brain development. In addition, the virus has been tied to Guillain Barré Syndrome in adults, which can cause temporary paralysis. The evidence on that, too, is mounting, but not yet conclusive, he said.

"With each passing day, the linkage between Zika and microcephaly becomes stronger," he said, adding that the same is true for the tie between Zika and Guillain Barré Syndrome.

"I wish we knew more about Zika today. I wish we could do more about Zika today," Frieden said.

A surge in microcephaly and Guillain Barré cases has been reported in Brazil, which is the epicenter of the Zika outbreak, since October of 2015. Outside of Brazil, there have been cases, including one microcephaly case involving a returning traveler from Brazil to Hawaii, but the time between infection and birth means that countries such as Colombia, where Zika transmission has recently been detected, have not yet seen an increase in such cases, Frieden said.

"We are quite literally discovering more about it each and every day."

To illustrate how rare the Zika connection to microcephaly would be, Frieden said that if proven, Zika would be the first virus in more than 50 years to cause a birth-related abnormality. He also said he is unaware of any other mosquito-borne illness that is linked with birth defects such as microcephaly.

Focus remains on mosquito transmission

Although sexual transmission of Zika virus infection is possible, mosquito bites from the widely distributed Aedes aegypti mosquito remain the primary way that Zika virus is transmitted. Because there is currently no vaccine or treatment for Zika virus, the best way to avoid Zika virus infection is to prevent mosquito bites.

In this Feb. 1, 2016 photo, Guilherme Trivellato, from the British biotec company Oxitec, releases genetically modified Aedes aegypti mosquitoes, a vector for transmitting the Zika virus, in Piracicaba, Brazil, as part of an effort to kill the local Aedes population.

Image: Andre Penner/AP

While the CDC's main focus is on preventing pregnant women from being infected with the virus, the new guidelines also include recommendations for non-pregnant women, and men with non-pregnant sexual partners who live in or have traveled to Zika-affected areas.

Here is the CDC's advice for this category of people:

In the interim guidance issued Friday morning, the CDC admits that doctors do not know how long the risk of sexual transmission lasts. More specifically, doctors don't know how long the virus can reside in bodily fluids, such as male semen.

Call for testing all pregnant women or women of reproductive age who want to be tested

The updated guidelines recommend that pregnant women without symptoms of Zika virus disease can be offered testing for the virus at anytime between two to 12 weeks after returning from areas with ongoing Zika virus transmission.

The CDC's Frieden said that at least initially there will be a shortage of testing capacity that may be frustrating for some women, but that testing capabilities are being scaled up quickly.

Here is the CDC's advise for women of reproductive age who are not planning on getting pregnant, but are worried about Zika exposure:

The CDC has issued travel advisories warning pregnant women to postpone travel to the majority of Central America and many South American nations and territories, from Costa Rica to Brazil, until more is known about the risks of contracting Zika and a resulting poor birth outcome such as microcephaly.